Numerous types of seals and sealing methods are known in the prior art. Seals are commonly used for sealing gaps and spaces between adjacent components. In many situations the primary function of the seal is to enable relative movement of the adjacent components while minimizing flow of fluids between such elements. The relatively movable components are commonly subject to static and dynamic forces, including forces produced by relative movement of the components as well as forces produced by vibrations, fluid pressure and thermal expansion and contraction. Numerous factors affect the ability of a seal to effectively seal an area between adjacent components, including environmental conditions, seal resiliency, flexibility of the seal the thermal conductivity and expansion of adjacent components, seal seating, seal hysteresis, and other factors.
For example in advanced aerospace engines and vehicles, seals are desired which have the properties of high compressive strength and yet seal effectively throughout a broad temperature range. The components of such advanced aerospace engines and vehicles, are often comprised of ceramics, exotic metals, or composites capable of maintaining structural integrity at extremely high temperatures, often in excess of 1500 degrees Fahrenheit. For these reasons, advanced aerospace engines and vehicles require high temperature resilient seals to minimize fluid flow between adjacent components and/or to minimize engine purge/coolant requirements. Dimensional changes between components due to temperature variations during operation and the adjacent positioning of components made of materials having widely different coefficients of thermal expansion (CTE), require seals that maintain resiliency and resistance to fluid flow through a broad range of dimensional and temperature changes. Seals employed in such applications are required to maintain preload with adjacent components during transient and steady-state conditions.
The seals known in the prior art to have some deficiencies limiting their ability to meet design requirements in applications such as advanced aerospace engines and vehicles, and other applications which require sealing between relatively movable components comprised of dissimilar materials which undergo repeated high temperature cycling. Some conventional braided rope seals such as disclosed in U.S. Pat. No. 5,358,262 provide resiliency, or spring-back, for short-term applications. However, as advanced alloy materials such as intermetallics (e.g. nickel-aluminides, titanium-aluminides, etc.), carbon-carbon composites, and ceramic matrix composites find use in advanced aerospace structures, and other devices requiring extended use over a plurality of cycles, seals are required that exhibit significantly higher levels of resiliency without sacrificing temperature capability.
Some braided rope seals such as disclosed in U.S. Pat. No. 5,358,262 have an inner metallic braided sheath and an external ceramic sheath. Such seals are used as a high temperature seal between a ceramic component and a metallic component. The seal member includes a multi-layer 0-ring seal composed of a bundle of uniaxial elongate ceramic fibers over-laid by a sheath of braided metal wire that is over-laid by a sheath of braided ceramic fibers.
U.S. Pat. No. 5,332,239 discloses a bellows seal made of a central bellows with a plurality of convolutions therein. The bellows is over-laid by a braided ceramic sheath which is over-laid by an outer abrasion-resistant sheath. A coolant may be circulated through the hollow interior of the bellows.
U.S. Pat. No. 5,301,595 discloses a high temperature rope seal for joint packing having a cylindrical core made of bundled and twisted ceramic fibers. The core is covered by a metallic cover made of a plurality of cross woven strands. Each cross woven strand includes a plurality of round stainless steel wires arranged side-by-side.
U.S. Pat. No. 5,082,293 discloses a high temperature, flexible, fiber-preform seal mounted in a groove in a moveable panel structure. The seal has a uniaxial core with a plurality of fibers encircled by an internal layer of spiral wound fibers. This internal layer is encircled by a plurality of left-hand and right-hand helical fibers that are encircled by an external layer of spiral wound fibers.
U.S. Pat. No. 4,576,081 discloses a ceramic sealing rope with one or more sleeves of woven cross wire surrounding a core strand. Each core strand comprises a plurality of yarns where each yarn surrounds a solid metal wire.
U.S. Pat. No. 1,078,333 discloses a low performance packing material having a core of longitudinally extending fiber and rubber strands. The core of the packing material is covered by an intermediate layer of wound fiber and rubber strands. The intermediate layer is covered with an outer wrap of fiber strands.
U.S. Pat. No. 5,161,806 shows a resilient seal construction which has a canted coil spring surrounding a hollow core. The areas intermediate of the spring coils are filled with a resilient material to block fluid flow between the coils.
None of these prior art seals have properties which perform as well as would be desirable in applications which require sealing between relatively movable components comprised of dissimilar materials which undergo repeated high temperature cycling to temperatures ranging to about 1500 degrees Fahrenheit.
Thus there exists a need for a sealing article and method, that provides enhanced fluid resistance, greater resiliency, improved maintenance of preload with adjacent components, greater flexibility, high load bearing capability, reduced permanent set, less hysteresis, and longer life, when used in sealing between components in advanced aerospace engines and vehicles and other devices which are subjected to extreme thermal changes.